Sometime in the next few weeks, Paul Brazelton will move his family into a 1935 Tudor in south Minneapolis that has no furnace. He's just finished a massive renovation of the family home and even though winter's bearing down, he removed the boiler and plans to use that basement space for his daughters' home-school classroom.

He also took out the fireplace.

If this sounds like the most uninviting house (and classroom) in Minneapolis, there's something else to know: Brazelton, a software engineer and passionate environmentalist, has nearly finished a retrofit of his house to the stringent engineering standards of the Passivhaus model, a German system of homebuilding that uses insulation and highly efficient doors and windows to save energy.

The finished 2,000-square-foot home could be warmed even in the dead of winter with a pair of small space heaters, Brazelton said, though the family plans to piggyback on their hot water heater and use an in-floor heating system in the basement.

"We're really nervous," said Brazelton, half-joking, "because when it's 20 degrees below and you can feel your house contracting and cracking like it's just trying to resist the cold, it's hard to believe that two space heaters from Target will do the trick for us."

The finished project is on track to be certified by the Passivhaus institute of Darmstadt, Germany, as the first "EnerPHit" home in North America, according to their architect Tim Eian of TE Studio in Minneapolis.

The EnerPHit standard, designed for existing homes, has been used thousands of times in Europe, said Eian, a German native. Such homes see their energy use fall from 75 to 90 percent.

Old home, new ideas

Brazelton and his wife, Desiree, have remodeled two other homes before, but never on the scale of the house he's working on now, nestled in a neighborhood near Lake Nokomis.

When they found it more than four years ago, the three-bedroom house had outdated mechanical systems and an awkward layout. A year ago they had "one-time" money and decided on an addition, but their plans quickly grew.

Brazelton, looking for ideas, toured a Passive House in Hudson and came away impressed. Six months into the design, Eian called to say he had run their latest plan through a computer program and it showed that the Brazelton home could meet the EnerPHit standard.

"That kind of captured our imaginations and short-circuited the logical part of our brain and went directly to the emotional excited part and we were like, 'Let's do it,'" said Brazelton.

New here, practiced elsewhere

The core idea of a Passive House is that it's so well insulated that it doesn't require a lot of energy. Triple-paned windows, highly efficient doors, and loads and loads of insulation make the house incredibly airtight. A mechanical ventilator blows fresh air in and stale air out. A heat exchanger takes the heat out of the outgoing air and adds it to the incoming air to minimize heat loss.

A heavy-duty retrofitting of this type can run $50 to $100 per square foot, said Eian. A new 1,750-square-foot house built to Passive House standards would take about 15 years to pay off the extra cost of insulation, windows and doors, Eian estimated.

Desiree and the Brazeltons' three daughters moved in with relatives as the work started this summer. Stucco was removed from the exterior. The rotting chimney was torn down. Heavy machinery dug a trench around the basement foundation.

What followed was a complicated process of adding insulation so that the home's shell -- everything from the attic to the exterior walls to the basement slab -- would be wrapped in insulation. The slab was broken up so that EPS foam could be laid under the house. The exterior walls were given vertical wooden ribs every few inches to hold the 9 1/2 inches of cellulose that would be required. The exterior walls will have an R44 rating. The attic will hit R80.

Brazelton is doing much of the traditional renovation work himself, with the help of his father and a few friends. He sleeps inside the unheated, unfinished house on a cot, sometimes with the family's two dogs for companions.

The more complicated work is being handled by a professional builder, Ryan Stegora. Stegora's never done this type of retrofit, said Brazelton, but has learned quickly.

Brazelton also talked to a marketing designer, someone who could help him navigate the building industry and connect with suppliers. Sensing that Brazelton's home will serve as a model, some companies have offered home building products at a discount. That's helped offset the added cost of shipping some of the home's parts from Germany, including vacuum-insulated panels, triple-paned windows and the ventilator.

A website (www.minnephithouse.com) lists the companies involved. Brazelton blogs there about the home's progress, when he's not building, being a father or tending to his day job.

"I told my wife after this is done I'm going to check myself into a psych ward to decompress," he said.

Matt McKinney • 612-217-1747

Matt McKinneyis a reporter on the Star Tribune's state team. In 15 years at the Star Tribune, he has covered business, agriculture and crime.